A cellular communication system provides wireless communication services to mobile users. The coverage area of the system is generally divided into a plurality of cells of substantially the same size. Each of the cells includes a base station that connects the mobile users in the cell to remote destinations. The base station provides wireless connections to the mobile users within the same cell. The base station also relays the connections to the remote destinations, typically via other base stations, over landlines, the public switched telephone network (PSTN), or a combination of wireless and wired backbone networks. The base station also allocates resources to the mobile users within the cell. The resource allocations may include time slot assignments, frequency allocations, and QoS (Quality of Service) assurance.
A mobile user may travel away from a first cell to enter a second cell. When that occurs, the mobile user's signal received at the base station of the first cell (i.e., the current base station) may become so weak in power that the signal becomes highly susceptible to interference and noise. To maintain the quality of the connection, the current base station may hand over the connection to the base station of the second cell (i.e., the target base station). The target base station may establish a new connection for the mobile user without alerting the user. This process of handing over a connection from the current base station to the target base station is called a hand-off process.
The hand-off process is generally initiated by the current base station. The current base station first requests the target base station allocate resources for the mobile user with a QoS level acceptable to the user. The target base station then sets up a new connection for the mobile user with the requested QoS. After the new connection is set up, the current base station tears down the current connection to the user, thus completing the hand-off process.
The hand-off process is generally required to be completed in a timely manner to avoid dropping calls or creating glitches. For multi-media transmissions, a delay in the hand-off process around 600–800 ms may cause a loss of approximately 20–38 typical video frames or 30–40 typical voice speech frames.